Novel catalyst mixtures

ABSTRACT

Catalysts comprised of at least one catalytically active element and at least one helper catalyst are disclosed. The catalysts may be used to increase the rate, the selectivity or lower the overpotential of chemical reactions. These catalysts may be useful for a variety of chemical reactions including in particular the electrochemical conversion of carbon dioxide to formic acid.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority to and the benefit under 35 U.S.C.§119(e) to provisional application 61/317,955, filed Mar. 26, 2010, thedisclosure of which is expressly incorporated herein by reference in itsentirety.

FIELD OF THE INVENTION

The field of the invention is catalysis and catalysts. The catalysts ofthis invention are applicable, for example, to the electrochemicalconversion of carbon dioxide into formic acid.

BACKGROUND

There is a present need to decrease carbon dioxide (CO₂) emissions fromindustrial facilities. Over the years, a number of electrochemicalprocesses have been suggested for the conversion of CO₂ into usefulproducts. Processes for CO₂ conversion and the catalysts for them arediscussed in U.S. Pat. Nos. 3,959,094 4,240,882 4,523,981 4,545,872,4,595,465 4,608,132 4,608,133 4,609,441 4,609,440, 4,620,906, 4,668,349,4,673,473, 4,711,708, 4,756,807, 4,756,807, 4,818,353 5,064,7335,284,563 5,382,332 5,709,789, 5,928,806, 5,952,540 6,024,855 6,660,6806,987,134 (the '134 patent), 7,157,404, 7,378,561, 7,479,570, patentapplication 20080223727 (The '727 application) and papers reviewed byHori (Modern Aspects of Electrochemistry, 42, 89-189, 2008) (“The HoriReview”), Gattrell, et al. (Journal of Electroanalytical Chemistry, 594,1-19, 2006) (“The Gattrell Review”), DuBois (Encyclopedia ofElectrochemistry, 7a, 202-225, 2006) (“The DuBois Review”), and thepapers Li, et al. (Journal of Applied Electrochemistry, 36, 1105-1115,2006, Li, et al. (Journal of Applied Electrochemistry, 37, 1107-1117,2007, and Oloman, et al. (ChemSusChem, 1, 385-391, 2008) (“The Li andOloman Papers”)

Generally an electrochemical cell contains an anode (50), a cathode (51)and an electrolyte (53) as indicated in FIG. 1. Catalysts are placed onthe anode, and or cathode and or in the electrolyte to promote desiredchemical reactions. During operation, reactants or a solution containingreactants is fed into the cell. Then a voltage is applied between theanode and the cathode, to promote an electrochemical reaction.

When an electrochemical cell is used as a CO₂ conversion system, areactant comprising CO₂, carbonate or bicarbonate is fed into the cell.A voltage is applied to the cell and the CO₂ reacts to form new chemicalcompounds. Examples of cathode reactions in The Hori Review include

CO₂+2e−→CO+O²⁻

2CO₂+2e−→CO+CO₃ ²⁻

CO₂+H₂O+2e−→CO+2OH⁻

CO₂+2H₂O+4e−→HCO ⁻+3OH⁻

CO₂+2H₂O+2e−→H₂CO+2OH⁻

CO₂+H₂O+2e−→(HCO₂)⁻+OH⁻

CO₂+2H₂O+2e−→H₂CO₂+2OH⁻

CO₂+6H₂O+6e−→CH₃OH+6OH⁻

CO₂+6H₂O+8e−→CH₄+8OH⁻

2CO₂+8H₂O+10e−→C₂H₄+12OH⁻

2CO₂+9H₂O+10e−→CH₃CH₂OH+12OH⁻

2CO₂+6H₂O+8e−→CH₃COOH+8OH⁻

2CO₂+5H₂O+8e−→CH₃COO⁻+7OH⁻

2CO₂+10H₂O+10e−→C₂H₆+14OH⁻

CO₂+2H⁺+2e−→CO+H₂O acetic acid, oxylic acid, oxylate

CO₂+4H⁺+4e−→CH₄

where e− is an electron. The examples given above are merelyillustrative and are not meant to be an exhaustive list of all possiblecathode reactions.

Examples of reactions on the anode mentioned in The Hori Review include

2O²⁻→O₂+4e−

2CO₃ ²→O₂+CO₂+4e−

4OH⁻→O₂+2H₂O+4e−

2H₂O→O₂+2H⁺+2e−

The examples given above are merely illustrative and are not meant to bean exhaustive list of all possible anode reactions.

In the previous literature, catalysts comprising one or more of V, Cr,Mn, Fe, Co, Ni, Cu, Sn, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re,Ir, Pt, Au, Hg, Al, Si, C, In, Sn, Tl, Pb, Bi, Sb, Te, U, Sm, Tb, La,Ce, and Nd have all shown activity for CO₂ conversion. Reviews includeMa, et al. (Catalysis Today, 148, 221-231, 2009) Hori (Modern Aspects ofElectrochemistry, 42, 89-189, 2008), Gattrell, et al. (Journal ofElectroanalytical Chemistry, 594, 1-19, 2006), DuBois (Encyclopedia ofElectrochemistry, 7a, 202-225, 2006) and references therein.

The results in The Hori Review show that the conversion of CO₂ is onlymildly affected by solvent unless the solvent also acts as a reactant.Water can act like a reactant, so reactions in water are different thanreactions in non-aqueous solutions. But the reactions are the same inmost non-aqueous solvents, and importantly, the overpotentials arealmost the same in water and in the non-aqueous solvents.

Zhang, et al. (ChemSusChem, 2, 234-238, 2009) and Chu, et al.(ChemSusChem, 1, 205-209, 2008) report CO₂ conversion catalyzed by anionic liquid. Zhao, et al. (The Journal of Supercritical Fluids, 32,287-291, 2004) and Yan et al Electrochimica Acta 54 (2009) 2912-2915report the use of an ionic liquid as a solvent and electrolyte, but nota co-catalyst, for CO₂ electroconversion. Each or these papers areincorporated by reference. The catalysts have been in the form of eitherbulk materials, supported particles, collections of particles, smallmetal ions or organometallics. Still according to Bell Basic ResearchNeeds, Catalysis For Energy, US Department Of Energy Report PNNL-17214,2008), (“The Bell Report”) “The major obstacle preventing efficientconversion of carbon dioxide into energy-bearing products is the lack ofcatalyst” with sufficient activity at low overpotentials and highelectron conversion efficiencies.

The overpotential is associated with lost energy of the process and soone needs the overpotential to be as low as possible. Yet, according toThe Bell Report “Electron conversion efficiencies of greater than 50percent can be obtained, but at the expense of very high overpotentials”This limitation needs to be overcome before practical processes can beobtained.

The '134 patent also considers the use of salt (NaCl) as a secondary“catalyst” for CO₂ reduction in the gas phase but salt does not lowerthe overpotential for the reaction.

A second disadvantage of many of the catalysts is that they also havelow electron conversion efficiency. Electron conversion efficienciesover 50% are needed for practical catalyst systems.

The examples above consider applications for CO₂ conversion but theinvention overcomes limitations for other systems. For example somecommercial CO₂ use an electrochemical reaction to detect the presence ofCO₂. At present, these sensors require over 1-5 watts of power, which istoo high for portable sensing applications.

Finally, the invention considers new methods to form formic acid. Othermethods are discussed in U.S. Pat. Nos. 7,618,725, 7,612,233, 7.420088,7,351,860, 7,323,593, 7,253,316, 7,241,365, 7,138,545, 6,992,212,6,963,909, 6,955,743, 6,906,222, 6,867,329, 6,849,764, 6,841,700,6,713,649, 6,429,333, 5,879,915, 5,869,739, 5,763,662, 5,639,910,5,334,759, 5,206,433, 4,879,070, 4,299,891. These processes do not useCO₂ as a reactant.

BRIEF SUMMARY OF THE INVENTION

The invention provides a novel catalyst mixture that can overcome one ormore of the limitations of low rates, high overpotentials and lowelectron conversion efficiencies (i.e. selectivities) for catalyticreactions and high powers for sensors. The catalyst mixture includes atleast one Catalytically Active Element, and at least one HelperCatalyst. When the Catalytically Active Element and the Helper Catalystare combined the rate and/or selectivity of a chemical reaction can beenhanced over the rate seen in the absence of the Helper Catalyst. Forexample, the overpotential for electrochemical conversion ofcarbon-dioxide can be substantially reduced and the current efficiency(i.e. selectivity) for CO₂ conversion can be substantially increased.

The invention is not limited to catalysts for CO₂ conversion. Inparticular, catalysts that include Catalytically Active Elements andHelper Catalysts might enhance the rate of a wide variety of chemicalreactions. Reaction types include: homogeneously catalyzed reactions,heterogeneously catalyzed reactions, chemical reactions in chemicalplants, chemical reactions in power plants, chemical reactions inpollution control equipment and devices, chemical reactions in fuelcells, chemical reactions in sensors. The invention includes all ofthese examples. The invention also includes processes using thesecatalysts.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a typical electrochemical cell.

FIG. 2 is a schematic of how the potential of the system moves as itproceeds along the reaction coordinate in the absence of the ionicliquid if the system goes through a (CO₂)⁻ intermediate The reactioncoordinate indicates the fraction of the reaction that has completed. Ahigh potential for (CO₂)⁻ formation can create a high overpotential forthe reaction.

FIG. 3 illustrates how the potential could change when a helper catalystis used. In this case the reaction could go through a CO₂-EMIM complexrather than a (CO₂)⁻ substantially lowering the overpotential for thereaction.

FIGS. 4A, 4B and 4C illustrate some of the cations that may be used toform a complex with (CO₂)⁻

FIGS. 5A and 5B illustrates some of the anions that may stabilize the(CO₂)⁻ anion.

FIG. 6 illustrates some of the neutral molecules that may be used toform a complex with (CO₂)⁻

FIG. 7 shows a schematic of a cell used for the experiments in Examples1, 2, 3, 4 and 5.

FIG. 8 shows comparison of the cyclic voltametry for a blank scan wherethe catalyst was synthesized as in Example 1 where i) the EMIM-BF4 wassparged with argon and ii) a scan where the EMIM-BF4 was sparged withCO₂. Notice the large negative peak associated with CO₂ formation

FIG. 9 shows a series of Broad Band Sum Frequency Generation (BB-SFG)taken sequentially as the potential in the cell was scanned from +0. to−1.2 with respect to SHE.

FIG. 10 shows a CO stripping experiment done by holding the potential at−0.6 V for 10 or 30 minutes and them measuring the size of the COstripping peak between 1.2 and 1.5 V with respect to RHE.

FIG. 11 shows a comparison of the cyclic voltametry for a blank scanwhere the catalyst was synthesized as in Example 3 where i) thewater-choline iodide mixture was sparged with argon and ii) a scan wherethe water-choline iodide mixture was sparged with CO₂.

FIG. 12 shows a comparison of the cyclic voltametry for a blank scanwhere the catalyst was synthesized as in Example 4 where i) thewater-choline chloride mixture was sparged with argon and ii) a scanwhere the water-choline chloride mixture was sparged with CO₂.

FIG. 13 shows a comparison of the cyclic voltametry for a blank scanwhere the catalyst was synthesized as in Example 5 where i) thewater-choline chloride mixture was sparged with argon and ii) a scanwhere the water-choline chloride mixture was sparged with CO₂.

FIG. 14 shows a schematic of the sensor.

FIG. 15 shows a schematic of where EMBF4 is placed on the sensor.

FIG. 16 shows the current measured when the voltage on the sensor wasexposed to various gases, the applied voltage on the sensor was sweptfrom 0 to 5 volts at 0.1 V/sec.

FIG. 17 shows the resistance of the sensor, in nitrogen and in carbondioxide. The resistance was determined by measuring the voltage neededto maintain a current of 1 microamp. Time is the time from when thecurrent was applied.

DETAILED DESCRIPTION OF THE INVENTION

It is understood that the invention is not limited to the particularmethodology, protocols, and reagents, etc., described herein, as thesemay vary as the skilled artisan will recognize. It is also to beunderstood that the terminology used herein is used for the purpose ofdescribing particular embodiments only, and is not intended to limit thescope of the invention. It also is to be noted that as used herein andin the appended claims, the singular forms “a,” “an,” and “the” includethe plural reference unless the context clearly dictates otherwise.Thus, for example, a reference to “a linker” is a reference to one ormore linkers and equivalents thereof known to those skilled in the art.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meanings as commonly understood by one of ordinary skillin the art to which the invention pertains. The embodiments of theinvention and the various features and advantageous details thereof areexplained more fully with reference to the non-limiting embodimentsand/or illustrated in the accompanying drawings and detailed in thefollowing description. It should be noted that the features illustratedin the drawings are not necessarily drawn to scale, and features of oneembodiment may be employed with other embodiments as the skilled artisanwould recognize, even if not explicitly stated herein.

Any numerical values recited herein include all values from the lowervalue to the upper value in increments of one unit provided that thereis a separation of at least two units between any lower value and anyhigher value. As an example, if it is stated that the concentration of acomponent or value of a process variable such as, for example, size,angle size, pressure, time and the like, is, for example, from 1 to 90,specifically from 20 to 80, more specifically from 30 to 70, it isintended that values such as 15 to 85, 22 to 68, 43 to 51, 30 to 32etc., are expressly enumerated in this specification. For values whichare less than one, one unit is considered to be 0.0001, 0.001, 0.01 or0.1 as appropriate. These are only examples of what is specificallyintended and all possible combinations of numerical values between thelowest value and the similar manner.

Moreover, provided immediately below is a “Definition” section, wherecertain terms related to the invention are defined specifically.Particular methods, devices, and materials are described, although anymethods and materials similar or equivalent to those described hereincan be used in the practice or testing of the invention. All referencesreferred to herein are incorporated by reference herein in theirentirety.

DEFINITIONS

The term “electrochemical conversion of CO₂” as used here refers to anyelectrochemical process, where carbon dioxide, carbonate, or bicarbonateis converted into another chemical substance in any step of the process.

The term “CV” as used here refers to a cyclic voltamogram or cyclicvoltammetry.

The term “Overpotential” as used here refers to the potential (voltage)difference between a reaction's thermodynamically determined reductionor oxidation potential and the potential at which the event isexperimentally observed.

The term “Cathode Overpotential” as used here refers to theoverpotential on the cathode of an electrochemical cell.

The term “Anode Overpotential” as used here refers to the overpotentialon the anode of an electrochemical cell.

The term “Electron Conversion Efficiency” refers to selectivity of anelectrochemical reaction. More precisely, it is defined as the fractionof the current that is supplied to the cell that goes to the productionof a desired product.

The term “Catalytically Active Element” as used here refers to anychemical element that can serve as a catalyst for the electrochemicalconversion of CO₂.

The term “Helper Catalyst” refers to any organic molecule or mixture oforganic molecules that does at least one of the following:

1) Speeds up an electochemical reaction

2) Lowers the overpotential of the reaction

without being substantially consumed in the process.

The term “Active Element, Helper Catalyst Mixture” refers to any mixturethat includes one or more Catalytically Active Element and at least oneHelper Catalyst

The term “Ionic Liquid” refers to salts or ionic compounds that formstable liquids at temperatures below 200° C.

The term “Deep Eutectic Solvent” refers to an ionic solvent thatincludes of a mixture which forms a eutectic with a melting point lowerthan that of the individual components.

Specifics

The invention relates generally to Active Element, Helper CatalystMixtures where the mixture does at least one of the following:

Speeds up a chemical reaction

Lowers the overpotential of the reaction

without being substantially consumed in the process.

For example such mixtures can lower the overpotential for CO₂ conversionto a value less than the overpotentials seen when the same CatalyticallyActive Element is used without the Helper Catalyst.

According to The Hori Review, Gattrell, et al. (Journal ofElectroanalytical Chemistry, 594, 1-19, 2006), DuBois (Encyclopedia ofElectrochemistry, 7a, 202-225, 2006) and references therein, catalystsinclude one or more of V, Cr, Mn, Fe, Co, Ni, Cu, Sn, Zr, Nb, Mo, Ru,Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Ir, Pt, Au, Hg, Al, Si, In, Sn, Tl, Pb,Bi, Sb, Te, U, Sm, Tb, La, Ce, and Nd all show activity for CO₂conversion. Products include one or more of CO, OH⁻, HCO⁻, H₂CO,(HCO₂)⁻, H₂CO₂, CH₃OH, CH₄, C₂H₄, CH₃CH₂OH, CH₃COO⁻, CH₃COOH, C₂H₆, CH₄,O₂, H₂(COOH)₂, (COO⁻)₂. Therefore, V, Cr, Mn, Fe, Co, Ni, Cu, Sn, Zr,Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Ir, Pt, Au, Hg, Al, Si, In,Sn, Tl, Pb, Bi, Sb, Te, U, Sm, Tb, La, Ce, and Nd are each examples ofCatalytically Active Elements but the invention is not limited to thislist of chemical elements. Possible products of the reaction are includeone or more of CO, OH⁻, HCO⁻, H₂CO, (HCO₂)⁻, H₂CO₂, CH₃OH, CH₄, C₂H₄,CH₃CH₂OH, CH₃COO⁻, CH₃COOH, C₂H₆, CH₄, O₂, H₂(COOH)₂, (COO⁻)₂, but theinvention is not limited to this list of products.

The Hori Review also notes that Pb. Hg, Tl, In, Cd, Bi. Zr, Cr, Sn and Ware best for formic acid production. Furuya, et al. (Journal ofElectroanalytical Chemistry, 431, 39-41, 1997) notes that Pd/Ru is alsoactive.

The Hori Review notes that there has been over 30 years of work on theelectrochemical conversion of CO₂ into saleable products, but still,according to page 69 of The Bell Report “Electron conversionefficiencies of greater than 50 percent can be obtained, but at theexpense of very high overpotentials” This limitation needs to beovercome before practical processes can be obtained.

FIGS. 2 and 3 illustrate one possible mechanism by which a HelperCatalyst can enhance the rate of CO₂ conversion. According toChandrasekaran, et al. (Surface Science, 185, 495-514, 1987) the highoverpotentials for CO₂ conversion occur because the first step in theelectroreduction of CO₂ is the formation of a (CO₂) intermediate. Ittakes energy to form the intermediate as illustrated in FIG. 2. Thisresults in a high overpotential for the reaction.

FIG. 3 illustrates what might happen if a solution containing1-ethyl-3-methylimidazolium (EMIM⁺) cations is added to the mixture.EMIM⁺ might be able to form a complex with the (CO₂)⁻ intermediate. Inthat case, the reaction could proceed via the EMIM⁺-(CO₂)⁻ complexinstead of going through a bare (CO₂)⁻ intermediate as illustrated inFIG. 3. If the energy to form the EMIM⁺-(CO₂)⁻ complex is less than theenergy to form the (CO₂)⁻ intermediate, the overpotential to for CO₂conversion could be substantially reduced. Therefore any substanceincluding EMIM⁺ cations could act as a Helper Catalyst for CO₂conversion.

Those trained in the state of art should recognize that in most cases,solvents only have small effects on the progress of catalytic reactions.The interaction between a solvent and an adsorbate is usually muchweaker than the interaction with a Catalytically Active Element, so thesolvent only makes a small perturbation to the chemistry occurring onmetal surfaces. The diagram in FIG. 3 postulates that such an effectcould be large.

Of course a Helper catalyst, alone, will be insufficient to convert CO₂.Instead, one still needs a Catalytically Active Element that cancatalyze reactions of (CO₂) in order to get high rates of CO₂conversion. Catalysts include at least one of the followingCatalytically Active Elements have been previously reported to be activefor electrochemical conversion of CO₂

-   -   V, Cr, Mn, Fe, Co, Ni, Cu, Sn, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd,        Hf, Ta, W, Re, Ir, Pt, Au, Hg, Al, Si, In, Sn, Tl, Pb, Bi, Sb,        Te, U, Sm, Tb, La, Ce, and Nd.        Many of these catalysts also show activity for a number of other        reactions. All of these elements are specifically included as        Catalytically Active Elements for the purposes of the invention.        This list of elements is meant for illustrative purposes only,        and is not meant to limit the scope of the invention.

Further, those skilled in the art should realize that the diagram inFIG. 3 could be drawn for any molecule that could form a complex with(CO₂)⁻. Previous literature indicates that solutions including one ormore of: ionic liquids, deep eutectic solvents, amines, and phosphines,including specifically imidazoniums, pyridiniums, pyrrolidiniums,phosphoniums, ammoniums sulfoniums, prolinates, methioninates, formcomplexes with CO₂. Consequently, they may serve as Helper Catalysts.Also Davis Jr, et al. (In ACS Symposium Series 856: Ionic Liquids asGreen Solvents Progress and Prospects, 100-107, 2003) list a number ofother salts that show ionic properties. Specific examples includecompounds including one or more of Acetocholines, alanines,aminoacetonitriles, methylammoniums, arginines, aspartic acids,threonines, chloroformamidiniums, thiouroniums, quinoliniums,pyrrolidinols, serinols, benzamidines, sulfamates, acetates, carbamates,triflates, and cyanides. These salts may act as helper catalysts. Theseexamples are meant for illustrative purposes only, and are not meant tolimit the scope of the invention.

Of course, not every substance that forms a complex with (CO₂)⁻ will actas a helper catalyst. Masel (Chemical Kinetics and Catalysis, Wiley2001, p717-720), notes that when an intermediate binds to a catalyst,the reactivity of the intermediate decreases. If the intermediate bondstoo strongly to the catalyst, the intermediate will become unreactive,so the substance will not be effective. This provides a key limitationon substances that act as helper catalysts. The helper catalyst cannotform too strong of a bond with the (CO₂)⁻ that the (CO₂)⁻ is unreactivetoward the Catalytically Active Element.

More specifically, one wishes the substance to form a complex with the(CO₂)⁻ so is that the complex is stable (i.e. has a negative free energyof formation) at potentials less negative than −1 V with respect to SHE.However the complex should not be so stable, that the free energy of thereaction between the complex and the Catalytically Active Element ismore positive than about 3 kcal/mol.

For example Zhao, et al. (The Journal of Supercritical Fluids, 32,287-291, 2004) examined CO₂ conversion over copper in1-n-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF6) but FIG. 3in Zhao et al shows that the BMIM-PF6 did NOT lower the overpotentialfor the reaction (i.e. the BMIM-PF6 did not act as a Helper Catalyst)/This may be because the BMIM-PF6 formed such a strong bond to the (CO₂)⁻that the CO₂ was unreactive with the copper. Similarly Yuan et alElectrochimica Acta 54 (2009) 2912-2915 examined the reaction betweenmethanol and CO₂ in 1-butyl-3-methylimidazolium bromide (BMIM-Br). TheBMIM-Br did not act as a helper catalyst. This may be because thecomplex was too weak or that the bromine poisoned the reaction.

Solutions consisting of one or more of the cations in FIG. 4, the anionsin FIG. 5, the neutral species in FIG. 6, where R1, R2 and R3 include H,OH or any ligand containing at least on carbon atom are believed to formcomplexes with CO₂ or (CO₂ ⁻. Specific examples include: imidazoniums,pyridiniums, pyrrolidiniums, phosphoniums, ammoniums and sulfoniums,prolinates, methioninates. All of these examples might be able to beused as Helper Catalysts for CO₂ conversion and are specificallyincluded in the invention. These examples are meant for illustrativepurposes only, and are not meant to limit the scope of the invention.

Further the Helper Catalyst could be in any one of the following formsi) a solvent for the reaction, ii) an electrolyte, iii) an additive toany component of the system, or iv) something that is bound to at leastone of the catalysts in a system. These examples are meant forillustrative purposes only, and are not meant to limit the scope of theinvention.

Those trained in the state of the art should recognize that one mightonly need a tiny amount of the Helper Catalyst to have a significanteffect. Catalytic reactions often occur on distinct active sites. Theactive site concentration can be very low so in principle a small amountof Helper Catalyst can have a significant effect on the rate. One canobtain an estimate of how little of the helper catalyst would be neededto change the reaction from Pease et al, JACS 47, 1235 (1925)'s study ofthe effect of carbon monoxide (CO) on the rate of ethylene hydrogenationon copper. This paper is incorporated into this disclosure by reference.Pease et al found that 0.05 cc's (62 micrograms) of carbon monoxide (CO)was sufficient to almost completely poison a 100 gram catalyst towardsethylene hydrogenation. This corresponds to a poison concentration of0.0000062% by weight of CO in the catalyst. Those trained in the stateof the art know that if 0.0000062% by weight of the poison in aCatalytically Active element-poison mixture could effectively suppressesa reaction, then as little as 0.0000062% by weight of Helper Catalyst inan Active Element, Helper Catalyst Mixture could enhance a reaction.This provides a lower limit to the Helper Catalyst concentration in anActive Element, Helper Catalyst Mixture.

The upper limit is illustrated in Example 1 below where the ActiveElement, Helper Catalyst Mixture has approximately 99.999% by weight ofHelper Catalyst, and the helper catalyst can be an order of magnitudemore concentrated. Thus the range of Helper Catalyst concentrations forthe invention here may be 0.0000062% to 99.9999%

FIG. 3 only considered the electrochemical conversion of CO₂, but themethod is general. There are many examples where energy is needed tocreate a key intermediate in a reaction sequence. Examples include:homogeneously catalyzed reactions, heterogeneously catalyzed reactions,chemical reactions in chemical plants, chemical reactions in powerplants, chemical reactions in pollution control equipment and devices,chemical reactions in safety equipment, chemical reactions in fuelcells, and chemical reactions in sensors. Theoretically, if one couldfind a Helper Catalyst that forms a complex with a key intermediate therate of the reaction should increase. All of these examples are withinthe scope of the invention.

Specific examples of specific processes that may benefit with HelperCatalysts, include the electrochemical process to produce productsincluding one or more of Cl₂, Br₂, I₂, NaOH, KOH, NaClO, NaClO₃, KClO₃,CF₃COOH.

Further, the Helper Catalyst, could enhance the rate of a reaction evenif it does not form a complex with a key intermediate. Examples ofpossible mechanisms of action include the Helper Catalyst i) loweringthe energy to form a key intermediate by any means ii) donating oraccepting electrons or atoms or ligands, iii) weakening bonds orotherwise making them easier to break, iv) stabilizing excited states,v) stabilizing transition states, vi) holding the reactants in closeproximity or in the right configuration to react vii) block sidereactions. Each of these mechanisms are described on pages 707 to 742 ofMasel, Chemical Kinetics and Catalysis, Wiley, NY 2001. All of thesemodes of action are within the scope of the invention.

Also, the invention is not limited to just the catalyst. Instead itincludes any process or device that uses an Active Element, HelperCatalyst Mixture as a catalyst. Fuel cells are sensors are specificallyincluded in the invention.

Without further elaboration, it is believed that one skilled in the artusing the preceding description can utilize the invention to the fullestextent. The following examples are illustrative only, and not limitingof the disclosure in any way whatsoever. These are merely illustrativeand are not meant to be an exhaustive list of all possible embodiments,applications or modifications of the invention.

Specific Example 1 Using a Active Element, Helper Catalyst Mixtureincluding of Platinum and 1-ethyl-3-Methylimidazoilum Tetrafluoroborate(EMIM-BF₄) to Lowering the Overpotential for Electrochemical Conversionof CO₂ and Raising the Selectivity (Current Efficiency) of the Reaction

The experiments used the glass three electrode cell shown in FIG. 7. Thecell consisted of a Three neck flask (101), to hold the anode (108), andthe cathode (109). A silver/0.01 molar silver ion reference electrode(103) in acetnonitrile was connected to the cell through a LugginCappillary (102). The reference electrode (103) was fitted with a vycorfrit to prevent any of the reference electrode solution fromcontaminating the ionic liquid in the capillary. The reference electrodewas calibrated against the Fc/Fc⁺ redox couple. A conversion factor of+535 was used convert our potential axis to reference the StandardHydrogen Electrode (SHE). A 25×25 mm Platinum gauze (size 52) (113) wasconnected to the anode while a 0.33 cm² polycrystalline gold plug (115)was connected to the cathode.

Prior to the experiments all glass parts were put through a 1% Nochromixbath (2 hrs), followed by a 50/50 v/v Nitric Acid/Water bath (12 hrs),followed by rinsing with Millipore water. In addition the gold plug(115) and platinum gauze (113) were mechanically polished usingprocedures known to workers trained in the art. They were then cleanedin a sulfuric acid bath for 12 hours.

During the experiment a catalyst ink comprising a Catalytically ActiveElement, platinum was first prepared as follows: First 0.0056 grams ofJohnson-Matthey Hispec 1000 platinum black purchased from Alfa-Aesar wasmixed with 1 grams of milipore water and sonicating for 10 minutes toproduce a solution containing a 5.6 mg/ml suspension of platinum blackin Millipore water. A 25 μl drop of the ink was placed on the gold plugand allowed to dry under a heat lamp for 20 min, and subsequentlyallowed to dry in air for an additional hour. This yielded a catalystwith 0.00014 grams of Catalytically Active Element, a platinum, on agold plug. The gold plug was mounted into the three neck flask (101).Next a Helper Catalyst, EMIM-BF₄ (EMD chemicals) was to heated to 120°C. under a −23 inch Hg vacuum for 12 hours to remove residual water andoxygen. The concentration of water in the ionic liquid after thisprocedure was found to be ca. 90 mM by conducting a Karl-Fischertitration. (i.e. the ionic liquid contained 99.9999% of helper catalyst)13 grams of the EMIM-BF₄ was added to the vessel, creating an ActiveElement, Helper Catalyst Mixture that contained about 99.999% of theHelper Catalyst. The geometry was such that the gold plug formed ameniscus with the EMIM-BF₄ Next ultra-high-purity (UHP) Argon was fedthrough the sparging tube (104) and glass frit (112) for 2 hours at 200sccm to further remove any moisture picked up by contact with the air.

Next the cathode was connected to the working electrode connection in aSI 1287 Solatron electrical interface, the anode was connected to thecounter electrode connection and the reference electrode was connectedto the reference electrode connection on the Solartron. Then thepotential on the cathode was swept from −1.5 V versus a standardhydrogen electrode (SHE) to 1V vs. SHE and then back to −1.5 voltsversus SHE thirty times at a scan rate of 50 mV/s. The current producedduring the last scan is labeled as the “blank” scan in FIG. 8.

Next carbon dioxide was bubbled through the sparging tube at 200 sccmfor 30 minutes and the same scanning technique was used. That producedthe CO₂ scan in FIG. 8. Notice the peak starting at −0.2 volts withrespect to SHE, and reaching a maximum at −0.4 V with respect to SHE.That peak is associated with CO₂ conversion.

We have also used broad-band sum frequency generation (BB-SFG) to lookfor products of the reaction. We only detect our desired produce carbonmonoxide in the voltage range shown (i.e. the selectivity is about 100%)Oxylic acid is detected at higher potentials.

Tables 1 compares these results to results from the previous literature.The table shows the actual cathode potential. More negative cathodepotentials correspond to higher overpotentials. More precisely theoverpotential is the difference between the thermodynamic potential forthe reaction (about −0.2 V with respect to SHE) and the actual cathodepotential. The values of the cathode overpotential are also given in thetable. Notice that the addition of the Helper Catalyst has reduced thecathode overpotential (i.e. lost work) on platinum by a factor of 4.5and improved the selectivity to nearly 100%.

TABLE 1 A comparison of the data in example 1 to results in the previousliterature. Cathode Selectivity potential to carbon Catalytically versusCathode containing Reference active element SHE overpotential productsData Here Platinum + −0.4 V 0.2 V ~100% EMIM-BF₄ The Hori ReviewPlatinum + −1.07 V 0.87 V  0.1% table 3 water The Li and Oloman Tin −2.5to −3.2 V 2.3 to 3 V 40-70%  Papers and the ‘727 application

TABLE 2 The cathode potentials where CO₂ conversion starts on a numberof Catalytically Active Elements as reported in The Hori Review. CathodeCathode Cathode potential potential potential Metal (SHE) Metal (SHE)Metal (SHE) Pb −1.63 Hg −1.51 Tl −1.60 In −1.55 Sn −1.48 Cd −1.63 Bi−1.56 Au −1.14 Ag −1.37 Zn −1.54 Pd −1.20 Ga −1.24 Cu −1.44 Ni −1.48 Fe−0.91 Pt −1.07 Ti −1.60

Table 2 indicates the cathode potential needed to convert CO₂. Noticethat all of the values are more negative than −0.9 V. By comparison,FIG. 8 shows that CO₂ conversion starts at −0.2 V with respect to RHE,when the Active Element, Helper Catalyst Mixture is used as a catalyst.More negative cathode potentials correspond to higher overpotentials.This is further confirmation Active Element, Helper Catalyst Mixturesare advantageous for CO₂ conversion.

FIG. 9 shows a series of BB-SFG spectra taken during the reaction.Notice the peak at 2350 cm⁻¹. This peak corresponds to the formation ofa stable complex between the Helper Catalyst and (CO₂)⁻. It issignificant that the peak starts at −0.1 with respect to SHE. Accordingto The Hori Review, (CO₂)⁻ is thermodynamically unstable unless thepotential is more negative than −1.2 V with respect to SHE on platinum.Yet FIG. 9 shows that the complex between EMIM-BF₄ and (CO₂)⁻ is stableat −0.1 V with respect to SHE.

Those trained in the art should recognize that this result is verysignificant. According to The Hori Review, The Dubois Review andreferences therein, the formation of (CO₂)⁻ is the rate determining stepin CO₂ conversion to CO, OH⁻, HCO⁻, H₂CO, (HCO₂)⁻, H₂CO₃, CH₃OH, CH₄,C₂H₄, CH₃CH₂OH, CH₃COO⁻, CH₃COOH, C₂H₆, CH₄, O₂, H₂, (COOH)₂, (COO⁻)₂ onV, Cr, Mn, Fe, Co, Ni, Cu, Sn, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta,W, Re, Ir, Pt, Au, Hg, Al, Si, In, Sn, Tl, Pb, Bi, Sb, Te, U, Sm, Tb,La, Ce, and Nd. The (CO₂)⁻ is thermodynamically unstable at lowpotentials, which leads to a high overpotential for the reaction asindicated in FIG. 2. The data in FIG. 9 shows that one can form theEMIM-BF4-(CO₂) complex at low potentials. The complex isthermodynamically. Thus, the reaction can follow a low energy pathwayfor CO₂ conversion to CO, OH⁻, HCO⁻, H₂CO, (HCO₂)⁻, H₂CO₂, CH₃OH, CH₄,C₂H₄, CH₃CH₂OH, CH₃COO⁻, CH₃COOH, C₂H₆, CH₄, O₂, H₂, (COOH)₂, (COO⁻)₂ onV, Cr, Mn, Fe, Co, Ni, Cu, Sn, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta,W, Re, Ir, Pt, Au, Hg, Al, Si, In, Sn, Tl, Pb, Bi, Sb, Te, U, Sm, Tb,La, Ce, and Nd as indicated in FIG. 3.

Those trained in the state of the art also recognize that this effect isvery unusual. In most cases, the interaction between a solvent and anadsorbate is weak, so the solvent only makes a small perturbation to thechemistry occurring on metal surfaces. Here the effect is large.

In order to understand the economic consequences of this result, wecalculated the cost of the electricity needed to create 100,000 metrictons per year of formic acid via two processes, i) the process describedin The Li and Oloman Papers and the '727 application, and ii) a similarprocess using the catalyst in this example. In both cases we assumedthat the anode would run at +1.4 V with respect to SHE and thatelectricity would cost $0.06/kW-hr and we scaled the current to bereasonable. The results of the calculations are given in Table 2. Noticethat the calculations predict that the electricity cost will go down byalmost a factor of 5 if the new catalysts are used. These resultsdemonstrate the possible impact of the new catalysts disclosed here.

TABLE 3 A comparison of the projected costs using the catalyst in theThe Li and Oloman papers and the ‘727 application, and ii) a similarprocess using the catalyst in this example. Cathode Anode Net Yearlypotential, Potential, Potential Electricity Catalyst V (SHE) V (SHE) VSelectivity cost The Li and Oloman −3.2 1.2 4.4 0.6 $65,000,000 Papersand the ‘727 application Active Element, −0.4 1.2 1.6 1 $14,000,000Helper Catalyst Mixture

Specific Example 2 The Effect of Dilution on the ElectrochemicalConversion of CO₂

This example shows that water additions speed the formation of CO. Theexperiment used the Cell and procedures in Example 1, with the followingexception: a solution containing 98.55% EMIM-BF4 and 0.45% water wassubstituted for the 99.9999% EMIM-BF4 used in Example 1, the potentialwas held for 10 or 30 minutes at −0.6V with respect to RHE, and then thepotential was ramped positively at 50 mV/sec. FIG. 10 shows the result.Notice the peak at between 1.2 and 1.5 eV. This is the peak associatedwith CO formation and is much larger than in example 1. Thus theaddition of water has accelerated the formation of CO presumably byacting as a reactant.

Specific Example 3 Using a Active Element, Helper Catalyst Mixture thatinclude Palladium and choline Iodide to Lowering the Overpotential forElectrochemical Conversion of CO₂ in Water

The next example is to demonstrate that the invention can be practicedusing Palladium as an active element and Choline Iodide as a HelperCatalyst.

The experiment used the cell and procedures in Example 1, with thefollowing exceptions: ii) A 10.3% by weight of a Helper Catalyst,choline iodide in water solution was substituted for the1-ethyl-3-methylimidazolium tetrafluoroborate and ii) a 0.25 cm² Pd foilpurchased from Alfa Aesar was substituted for the gold plug and platinumblack on the cathode, and a silver/silver chloride reference was used.

FIG. 11 shows a CV taken under these conditions. There is a largenegative peak near zero volts with respect with SHE associated withiodine transformations and a negative going peak starting at about 0.8 Vassociated with conversion of CO₂. By comparison the data in Table 2indicates that one needs to use a voltage more negative that −1.2 V toconvert CO₂ on palladium in the absence of the Helper Catalyst. Thus,the helper catalyst has lowered the overpotential for CO₂ formation byabout 0.5 V.

This example also demonstrates that the invention can be practiced witha second active element, palladium, and a second helper catalyst cholineiodide. Further, those trained in the state of the art will note thatthere is nothing special about the choice of palladium and cholineiodide. Rather, this example shows that the results are general and notlimited to the special case in example 1.

Specific Example 4 Using a Active Element, Helper Catalyst Mixture thatincludes Palladium and Choline Chloride to Lowering the Overpotentialfor Electrochemical Conversion of CO₂ to Formic Acid

The next example is to demonstrate that the invention can be practicedusing a third Helper Catalyst, choline chloride.

The experiment used the Cell and procedures in Example 3, with thefollowing exception: a 6.5% by weight choline chloride in water solutionwas substituted for choline iodide solution.

FIG. 12 shows a comparison of the cyclic voltametry for a blank scanwhere i) the water-choline chloride mixture was sparged with argon andii) a scan where the water-choline iodide mixture was sparged with CO₂.Notice the negative going peaks starting at about −0.6. This shows thatCO₂ is being reduced at −0.6 V. By comparison the data in Table 2indicates that one needs to use a voltage more negative than −1.2 V isneeded to convert CO₂ on palladium in the absence of the HelperCatalyst. Thus, the overpotential for CO₂ conversion has been lowered by0.6 V by the Helper Catalyst.

Another important point is that there is no strong peak for hydrogenformation. A bare palladium, catalyst would produce a large hydrogenpeak at about −0.4 V at a pH of 7. While the hydrogen peak moves to −1.2V in the presence of the helper catalyst. The Hori Review reports thatpalladium is not an effective catalyst for CO₂ reduction because theside reaction producing hydrogen is too large. The data in FIG. 12 showthat the helper catalysts are effective in suppressing hydrogenformation.

We have also used CV to analyze the reaction products. Formic Acid wasthe only product detected. By comparison The Hori Review reports thatthe reaction is only 2.8% selective to formic acid in water. Thus theHelper Catalyst has substantially improved the selectivity of thereaction to formic acid.

This example also demonstrates that the invention can be practiced witha third helper catalyst choline chloride. Further, those trained in thestate of the art will note that there is nothing special about thechoice of palladium and choline chloride. Rather, this example showsthat the results are general and not limited to the special case inexample 1.

Specific Example 5 Using a Active Element, Helper Catalyst Mixture thatincludes nickel and Choline Chloride to Lowering the Overpotential forElectrochemical Conversion of CO₉ to CO

The next example is to demonstrate that the invention can be practicedusing a third metal, nickel.

The experiment used the Cell and procedures in Example 4, with thefollowing exception: a nickel foil from Alfa Aesar was substituted forthe palladium foil.

FIG. 13 shows a comparison of the cyclic voltametry for a blank scanwhere i) the water-choline chloride mixture was sparged with argon andii) a scan where the water-choline chloride mixture was sparged withCO₂. Notice the negative going peaks starting at about −0.6. This showsthat CO₂ is being reduced at −0.6 V. By comparison the data in Table 2indicates that one needs to use a voltage more negative than −1.48 V isneeded to convert CO₂ on nickel in the absence of the Helper Catalyst.Thus, the Helper Catalyst has lowered the overpotential for CO₂conversion.

Another important point is that there is no strong peak for hydrogenformation. A bare nickel, catalyst would produce a large hydrogen peakat about −0.4 V at a pH of 7. While the hydrogen peak moves to −1.2 V inthe presence of the helper catalyst. The Hori Review reports that nickelis not an effective catalyst for CO₂ reduction because the side reactionproducing hydrogen is too large. The data in FIG. 13 show that thehelper catalysts are effective in suppressing hydrogen formation.

Also the helper catalyst is very effective in improving the selectivityof the reaction. The Hori Review reports that hydrogen is the majorproduct during carbon dioxide reduction on nickel in aqueous solutions.The hydrolysis shows 1.4% selectivity to formic acid, and no selectivityto carbon monoxide. By comparison, analysis of the reaction products byCV indicate that carbon monoxide is the major product during CO₂conversion on nickel in the presence of the Helper Catalyst. There maybe some formate formation. However, no hydrogen is detected. Thisexample shows that the helper catalyst has tremendiously enhanced theselectivity of the reaction toward CO and formate.

This example also demonstrates that the invention can be practiced witha third metal, nickel. Further, those trained in the state of the artwill note that there is nothing special about the choice of nickel andcholine chloride. Rather, this example shows that the results aregeneral and not limited to the special case in example 1.

Those trained in the state of art should realize that since cholinechloride, and choline iodide are active, other chlorine salts such ascholine bromide, choline fluoride and choline acetate should be activetoo.

Specific Example 6 Demonstration that an Active Element (Gold), HelperCatalyst Mixture is useful in a CO₂ Sensor

This example demonstrates that the invention can be practiced with afourth active element gold. It also demonstrates that the catalysts areuseful in sensors.

The sensor will be a simple electrochemical device where an in an ActiveElement, Helper Catalyst Mixture is placed on an anode and cathode in anelectrochemical device, then the resistance of the sensor is measured.If there no CO₂ present, the resistance will be high, but not infinitebecause of leakage currents. When CO₂ is present, the Active Element,Helper Catalyst Mixture may catalyze the conversion of CO₂. That allowsmore current to flow through the sensor. Consequently, the sensorresistance decreases. As a result, the sensor may be used to detectcarbon dioxide.

An example sensor was fabricated on a substrate made from a 100 mmSilicon wafer (Silicon Quest, 500 μm thick, <100> oriented, 1-5 Ω·cmnominal resistivity) which was purchased with a 500 nm thermal oxidelayer. On the wafer, 170 Å chromium was deposited by DC magnetronsputtering (˜10 ⁻² Ton of argon background pressure). Next, 1000 Å of aCatalytically Active element, gold, was deposited on the chromium andthe electrode was patterned via a standard lift-off photolithographyprocess to yield the device shown schematically in FIG. 14.

At this point, the device consisted of an anode (200) and cathode (201)separated by a 6 μm gap, wherein the anode and cathode were coated witha Catalytically Active element, gold. At this point the sensor could notdetect CO₂.

Next 2 μl of a Helper Catalyst, EMIM BF₄ (202) was added over thejunction as shown FIG. 15. The device was mounted into a sensor testcell with wires running from the anode and cathode.

Next, the anode and cathode were connected to a SI 1287 Solatronelectrical interface, and the catalysts were condition by sweeping fromo volts to 5 volts at 0.1 V/sec and then back again. The process wasrepeated 16 times. Then the sensor was exposed to either nitrogen,oxygen, dry air or pure CO₂, and the sweeps were recorded. The lastsweep is shown in FIG. 16. Notice that there is a sizable peak at anapplied voltage of 4 volts in pure CO₂. That peak is associated with theelectrochemical conversion of CO₂.

Notice that the peak is absent, when the sensor is exposed to oxygen ornitrogen, but it is clearly seen when the sensor is exposed to aircontaining less than 400 ppm of CO₂. Further the peak grows as the CO₂concentration increases. Thus, the sensor can be used to detect thepresence of CO₂.

We have also run the sensor in a galvanastatic mode, were we measuredthe voltage needed to maintain the current constant at 1 microamp, andmeasured the voltage of the device. FIG. 17 shows that less voltage isneeded to maintain the current when CO₂ is added to the cell. This showsthat the sensor that include an Active Element, Helper Catalyst Mixtureresponds to the presence of CO₂.

Table 4 compares the sensor here to those in the previous literature.Notice that the new sensor uses orders of magnitude less energy thancommercial CO₂ sensors. This is a key advantage for many applications.

This example also illustrates that the invention can be practiced with athird active element, gold.

TABLE 4 A comparison of the power needed to run the present sensor tothat needed to operate commercially available CO₂ sensors. Sensor PowerSensor Power Specific 5 × 10⁻⁷ watts GE Ventostat 8100 1.75 wattsExample 3 Honeywell 3 watts Vaisala CARBOCAP about 1 watt C7232 GMP343

The examples given above are merely illustrative and are not meant to bean exhaustive list of all possible embodiments, applications ormodifications of the invention. Thus, various modifications andvariations of the described methods and systems of the invention will beapparent to those skilled in the art without departing from the scopeand spirit of the invention. Although the invention has been describedin connection with specific embodiments, it should be understood thatthe invention as claimed should not be unduly limited to such specificembodiments. Indeed, various modifications of the described modes forcarrying out the invention which are obvious to those skilled in thechemical arts or in the relevant fields are intended to be within thescope of the appended claims.

The disclosures of all references and publications cited above areexpressly incorporated by reference in their entireties to the sameextent as if each were incorporated by reference individually.

1. A electrocatalyst comprised of at least one Catalytically ActiveElement and at least one Helper Catalyst wherein the catalyst is activefor the electrochemical synthesis of formic acid using a reactantcomprised of carbon dioxide.
 2. The electrocatalyst in claim 1 where theCatalytically Active Element is comprised of one or more of Pb, Hg, Tl,In, Cd, Bi. Zr, Cr, Sn, W, Pd, Ru.
 3. The electrocatalyst in claim 1wherein The Helper Catalyst is comprised at least one of the following:phosphines, imidazoniums, pyridiniums, pyrrolidiniums, phosphoniums,sulfoniums, prolinates, methioninates, and cholines
 4. Theelectrocatalyst in claim 1 wherein the Helper Catalyst is comprised ofone or more of choline chloride, choline bromide, or choline iodide
 5. Acatalyst for the electrochemical conversion of CO₂ comprised of at leastone Catalytically Active Element and at least one Helper Catalyst
 6. Thecatalyst in claim 5 wherein the Catalytically Active Element comprisedof at least one of the following chemical elements: V, Cr, Mn, Fe, Co,Ni, Cu, Sn, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Ir, Pt, Au,Hg, Al, Si, C, In, Sn, Tl, Pb, Bi, Sb, Te, U, Sm, Tb, La, Ce, Nd
 7. Thecatalyst in claim 5 wherein the Helper Catalyst comprises at least oneorganic cation and or at least one organic anion.
 8. The catalyst inclaim 7 wherein the Helper Catalyst has a concentration of between about0.0000062% and 99.9999% by weight.
 9. The catalyst in claim 8 whereinThe Helper Catalyst is comprised at least one of the following:phosphines, imidazoniums, pyridiniums, pyrrolidiniums, phosphoniums,sulfoniums, prolinates, methioninates, and cholines
 10. The catalyst inclaim 5 wherein the Helper Catalyst is a solvent, electrolyte oradditive.
 11. A process for the formation of formic acid wherein carbondioxide reacts in an electrochemical cell containing a catalystcomprised of at least one Catalytically Active Element and at least oneHelper Catalyst.